The present invention relates to the production of amine salts of aromatic and aliphatic mono- and polycarboxylic acids. Such salts, as disclosed in our copending application Ser. No. 436,861, filed Jan. 28, 1974, have utility as intermediates in the preparation of the corresponding carboxylic acids and derivatives thereof, such as esters and anhydrides. Amine salts may also be useful in the separation of isomeric carboxylic acids. U.S. Pat. No. 2,664,440, for example, discloses the separation of isophthalic and terephthalic acids by conversion of the acids to the amine salts, which are more readily separated, by fractional crystallization, followed by reconversion to the acid.
Amine salts of carboxylic acids are usually produced by reacting the acid with an amine, often in aqueous solution. The usual commercial method of producing aromatic carboxylic acids and their anhydrides is by air oxidation of a corresponding lower alkyl (e.g. methyl-, ethyl- or propyl-) benzene, in the presence of a catalyst. Aliphatic carboxylic acids, both saturated and unsaturated, can also be made by air oxidation, in the presence of a catalyst, from the corresponding paraffin or olefin containing a terminal methyl group. Such processes generally result in the production of undesirable by-products, e.g., other carboxylic acids and aldehydes, in addition to the desired acid or anhydride. Generally, such by-products must be removed for the acid to be commercially useful.
Another method of producing carboxylic acids is by conversion of the corresponding hydrocarbons to nitriles, followed by conversion of the nitriles to acids, e.g. by hydrolysis. Aromatic carboxylic acids have been produced by both catalytic and non-catalytic hydrolysis of a corresponding nitrile, with stripping of ammonia from the hydrolysis product, and by hydrolysis to ammonium salts and thermal decomposition of the salts to the free acid. In such processes, however, large amounts of steam or other stripping gas and other utilities may be required. Additionally, subsequent purification of the acid may be required to eliminate nitrogenous by-products, such as intermediate products of the nitrile hydrolysis.
It has also been known to similarly produce various carboxylic acids, or ammonium salts thereof, by hydrolysis of the corresponding amides or imides.
It is an object of this invention to provide a new, improved process for hydrolysis of aromatic and aliphatic nitriles.
A second object of the present invention is to produce amine salts of aromatic and aliphatic mono-and polycarboxylic acids without requiring the production of the acid as an intermediate compound. Another object of the present invention is to provide amine salts for use as intermediates in the production of carboxylic acids and derivatives thereof. A third object of this invention is to produce amine salts of carboxylic acids from corresponding nitriles, amides, imides or mixtures thereof. Yet another object of this invention is to prepare amine salts of carboxylic acids from corresponding hydrocarbons. Still another objective of this invention is to provide amine salt intermediates for the production of carboxylic acids from corresponding hydrocarbons without also producing undesirable oxidation by-products.